diff --git a/projects/igniteui-angular/grids/grid/src/grid-base.directive.ts b/projects/igniteui-angular/grids/grid/src/grid-base.directive.ts index ee11fce0646..d6abade655f 100644 --- a/projects/igniteui-angular/grids/grid/src/grid-base.directive.ts +++ b/projects/igniteui-angular/grids/grid/src/grid-base.directive.ts @@ -3697,7 +3697,12 @@ export abstract class IgxGridBaseDirective implements GridType, this.throttleTime$.pipe( take(1), switchMap(time => timer(time, this.throttleScheduler)) - ) + ), + // `trailing: true` ensures the final settle position of a fast momentum + // scroll is processed; otherwise the last scroll events are dropped and the + // rows stay frozen at an intermediate startIndex while the scrollbar is at top. + // `leading: true` keeps the immediate response on scroll start. + { leading: true, trailing: true } ), destructor ) diff --git a/projects/igniteui-angular/grids/grid/src/grid.component.spec.ts b/projects/igniteui-angular/grids/grid/src/grid.component.spec.ts index 07b9e63e6c7..41d2fd7f13f 100644 --- a/projects/igniteui-angular/grids/grid/src/grid.component.spec.ts +++ b/projects/igniteui-angular/grids/grid/src/grid.component.spec.ts @@ -882,6 +882,73 @@ describe('IgxGrid Component Tests #grid', () => { expect(grid.verticalScrollContainer.getScroll().scrollTop).toBe(initialScroll); expect(grid.headerContainer.getScroll().scrollLeft).toBeGreaterThanOrEqual(2 * (initialHorScroll + 50)); })); + + describe('scroll throttle trailing edge', () => { + beforeEach(waitForAsync(() => { + TestBed.configureTestingModule({ + imports: [NoopAnimationsModule, IgxGridScrollThrottleComponent], + providers: [{ provide: SCROLL_THROTTLE_TIME_MULTIPLIER, useValue: 0 }] + }).compileComponents(); + })); + + // Drive scrollNotify directly (not programmatic scrollTop, whose async native events would mask a dropped-trailing regression) to exercise the throttle window deterministically. + it('should settle at the top row after a fast momentum scroll back to scrollTop 0', async () => { + const fix = TestBed.createComponent(IgxGridScrollThrottleComponent); + fix.detectChanges(); + await wait(50); + fix.detectChanges(); + const grid = fix.componentInstance.grid; + const virtDir = grid.verticalScrollContainer; + const scrollEl = virtDir.getScroll(); + const hScroll = grid.headerContainer.getScroll(); + const maxScroll = scrollEl.scrollHeight - scrollEl.clientHeight; + + // Guard the reproduction condition: the fixture must overflow horizontally. + expect(hScroll.scrollWidth).toBeGreaterThan(hScroll.clientWidth); + + // Move away from the top so the first rows are virtualized out of view. + grid.scrollNotify.next({ target: { scrollTop: maxScroll } }); + await wait(50); + fix.detectChanges(); + expect(virtDir.state.startIndex).toBeGreaterThan(0); + + // Momentum scroll back to top: intermediate on the leading edge, scrollTop = 0 settle only on the trailing edge. + grid.scrollNotify.next({ target: { scrollTop: Math.round(maxScroll / 2) } }); + grid.scrollNotify.next({ target: { scrollTop: 0 } }); + await wait(50); + fix.detectChanges(); + + // Without the trailing edge the settle is dropped and startIndex stays frozen mid-list. + expect(virtDir.state.startIndex).toBe(0); + expect(grid.gridAPI.get_row_by_index(0)).toBeDefined(); + }); + + it('should settle at the last row after a fast momentum scroll to the bottom', async () => { + const fix = TestBed.createComponent(IgxGridScrollThrottleComponent); + fix.detectChanges(); + await wait(50); + fix.detectChanges(); + const grid = fix.componentInstance.grid; + const virtDir = grid.verticalScrollContainer; + const scrollEl = virtDir.getScroll(); + const hScroll = grid.headerContainer.getScroll(); + const maxScroll = scrollEl.scrollHeight - scrollEl.clientHeight; + const lastIndex = fix.componentInstance.data.length - 1; + + expect(hScroll.scrollWidth).toBeGreaterThan(hScroll.clientWidth); + expect(virtDir.state.startIndex).toBe(0); + + // Momentum scroll top to bottom: intermediate on the leading edge, max-scroll settle only on the trailing edge. + grid.scrollNotify.next({ target: { scrollTop: Math.round(maxScroll / 2) } }); + grid.scrollNotify.next({ target: { scrollTop: maxScroll } }); + await wait(50); + fix.detectChanges(); + + // Without the trailing edge the settle is dropped and the last row is never brought into view. + expect((virtDir.state.startIndex ?? 0) + (virtDir.state.chunkSize ?? 0)).toBeGreaterThanOrEqual(lastIndex + 1); + expect(grid.gridAPI.get_row_by_index(lastIndex)).toBeDefined(); + }); + }); }); describe('IgxGrid - default rendering for rows and columns', () => { @@ -4051,3 +4118,19 @@ export class IgxGridPerformanceComponent implements AfterViewInit, OnInit { export class IgxGridNoDataComponent { @ViewChild(IgxGridComponent, { static: true }) public grid: IgxGridComponent; } + +@Component({ + template: ``, + imports: [IgxGridComponent] +}) +class IgxGridScrollThrottleComponent { + @ViewChild(IgxGridComponent, { static: true }) public grid: IgxGridComponent; + // 30 columns in a 600px-wide grid guarantee horizontal overflow, plus 200 rows for vertical virtualization. + public data = Array.from({ length: 200 }, (_row, rowIndex) => { + const record: Record = { ID: rowIndex }; + for (let col = 0; col < 30; col++) { + record[`Col${col}`] = `r${rowIndex}c${col}`; + } + return record; + }); +}